1. Field of the Invention
This invention relates to tire pressure indicating devices and has particular references to devices for signalling when the air pressure within a tire exceeds or drops below an optimum range.
2. Description of the Prior Art
As is well known, over inflation or under inflation of tires, particularly those of heavy vehicles such as trucks and buses, materially reduces the life of such tires and can cause blowouts and even fire damage due to overheating. Also, in cases where dual wheels are employed at different wheel positions, loss of pressure in one tire can cause loss of both tires before the operator can normally become aware of the situation since the excessive load applied to the remaining tire may cause extreme flexure and overheating thereof with the possibility of both tires blowing out or catching fire.
Systems have been developed heretofore for signalling to the operator when the pressure in any of the tires of his vehicle becomes over or under inflated. Such systems generally have not been satisfactory due to complexity of the systems and consequent high cost of manufacture and maintenance as well as unreliability. Such systems also have other drawbacks. For example, certain systems require dismantling of all or part of the signalling device in order to check or correct the tire pressure. Others are capable of signalling an over or under inflation condition only when the vehicle is moving. Again, other systems embody pressure sensing devices having considerable mass and these are therefore affected by centrifugal and vibratory or jarring forces imparted thereto by the wheels as they roll over the ground surface.